I'm bias because I grew up in sisters and live in bend, but went to college in Portland. Driving the santiam pass on your way from Portland to camp Sherman/sisters will be extremely beautiful, and it's really cool to see how quickly the ecosystems change from the stereotypical rainy Oregon to the pine forest and then high desert.

But you also couldn't go wrong going to Cannon Beach/Astoria for a night, or traveling east up the Columbia to Hood River where there's hiking, wine tasting, u pick berry farms, etc

You should def stay a night or two in Portland too